Lay statement: Ninety percent of the 500,000 annual new cases of Kala-azar or clinical visceral leishmaniasis (VL) occur in India/Bangladesh/Nepal, Sudan and Brazil. Clinical VL is associated with recurrent fever, hepatosplenomegaly, general lymphadenopathy, pancytopenia and anemia, and is fatal unless treated. However, ~80-90% of human infections result in asymptomatic or sub-clinical disease. The long-term objective of this project is to understand the genes and mechanisms that determine why two people with the same exposure to infection differ in susceptibility to clinical disease. This will provide important leads in determining improved strategies for therapeutic intervention. Project description: To identify genes/mechanisms/pathways that contribute to VL pathogenesis we will: (1) continue to build the resource of multicase families of VL for linkage studies, and case-parent trios for allelic association studies, throughout the course of the TMPC period, with the ultimate aim of building a minimum resource of 1000 case-parent trios that that can be used to re-evaluate previous candidate gene studies and to undertake a SNP-chip allelic association study;(2) refine map regions (minimally chromosomes 1p13.1, 2q12-q14.1, 6p25.3-p25.1, 8p23.1, 11q14.1-q22.3 and Xq21.31-q25) of the genome positive on a primary linkage genome scan for VL previously undertaken by us on Indian multicase families by genotyping additional micro-satellite markers in the primary and additional multicase families and carrying out linkage analysis;(3) genotype SNPs to determine Y chromosome haplotypes for founding males in families and use these as tags to look for lineage-specific susceptibility loci by stratifying the linkage analysis by Y chromosome haplotype;(4) identify the etiological genes under the peaks of linkage that remain positive after refined mapping by genotyping haplotype tagging SNPs in both multicase families and trios, and carrying out family based allelic association tests;(5) re-sequence the putative etiological genes that show allelic association under the linkage peaks to identify the functional variants associated with disease;and (6) study expression/localization of the products of all VL susceptibility genes (i.e. those identified in Indian and non-Indian populations) at RNA and protein levels in splenic biopsy material from patients, and/or peripheral blood cells with/without specific antigenic stimulation from patients and contacts.